KR20010033021A - Crystal growth - Google Patents

Abstract

The invention provides a mass of crystals, particularly diamond crystals, having a size of less than 100 microns and in which mass the majority of the crystals are faceted single crystals. The invention further provides a method of producing such a mass of crystals which utilizes crystal growth under elevated temperature and pressure conditions, the supersaturation driving force necessary for crystal growth being dependent, at least in part, on the difference in surface free energy between low Miller index surfaces and high Miller index surfaces of the crystals. Preferably, the method is carried out under conditions where the Wulff effect dominates.

Description

Crystalline growth {CRYSTAL GROWTH}

High temperature, high pressure synthesis of crystals, in particular diamond and equiaxed boron nitride, is well known. The two main methods used, both from solutions, are temperature gradient and allotrope conversion. In the temperature gradient method, the driving force of crystal growth is supersaturation due to the difference in solubility caused by the temperature difference between the raw material and the growth crystal. In the allotrope conversion method, the driving force for crystal growth is supersaturation due to the difference in solubility caused by the allotrope (or polymorph) difference between the raw material and the growth crystal.

Summary of the Invention

The present invention provides a crystal agglomerate, in particular a diamond crystal agglomerate, in which the crystal size is less than 100 micron and most, preferably at least 80%, of the crystal agglomerate is faceted single crystals visible to the naked eye. Some of the crystals may be twins.

Crystal agglomerates, which are primarily visually observable faceted monocrystals, provide a growing form of crystalline raw material that is substantially free of visually visible faceted surfaces, by contacting the raw material crystals with a suitable solvent / catalyst. Preparing a reaction agglomerate, applying the reaction agglomerate to an elevated temperature and elevated pressure suitable for crystal growth in a reaction zone of a high temperature / high pressure device, removing the reaction agglomerate from the reaction zone, and recovering crystals from the reaction agglomeration. And the crystal growth conditions can be prepared by a method in which the raw crystals are selected to be converted to crystals with developed facets that are visually observable with a low Miller index. The visible single faced crystals in the crystal mass are generally 80% or more.

The method of generating the supersaturation motive force necessary to grow the crystals used in the practice of the present invention is a surface between a surface with a lower Miller index and a surface with a higher Miller index, referred to below as the "wulff effect". At least partially, preferably predominantly, depends on the free energy difference; Surfaces with higher Miller indices have higher surface free energy than surfaces with lower Miller indices. An equilibrium form of the crystal is produced when the minimum value of the total surface free energy per unit volume of the crystal is reached, ie when the crystal is surrounded by a low Miller index surface. Surfaces with higher Miller indices can be considered to comprise a series of surfaces with lower Miller indices in close proximity to each other. The situation is included in the term "surface with higher Miller index". If the crystal is in its equilibrium form, there is a point where the vertical distance from all faces is proportional to the surface free energy of this face. This is the basis of Wolf's theory.

In diamond, which is a preferred crystal in the practice of the present invention, crystallization is continued when diamond crystals of various sizes including a large tens of microns and a large difference in surface free energy between surfaces with high Miller indices and surfaces with low Miller indices are used. Can cause supersaturation. Thus, the present invention is characterized by the difference in solubility of the crystal surface having a high Miller index and the crystal surface having a low Miller index, for example, characterizing the surface with a high Miller index macroscopically, substantially eliminating torsion and other structural defects. It has a special use for diamond crystal growth, in which supersaturation is at least partially preferably predominantly produced by reducing free energy.

In addition, the Wolf effect was observed to follow the prevailing conditions in the reaction mass. For example, when a given solvent / catalyst and pressure are applied, the wolf effect depends on temperature and time, as can be seen from the graphs shown in FIGS. 1 and 2. The graph of FIG. 1 shows the temperature dependence of the wolf effect on diamond in iron-nickel solvent / catalyst while maintaining at about 5.4 GPa for 1 hour. The graph of FIG. 2 shows the temperature dependence of the wolf effect on diamond in the same iron-nickel solvent / catalyst while maintaining at about 5.4 GPa for 10 hours. From the graph, it is noted that the larger the raw material crystal size and the higher the temperature applied, the more predominantly the Wolf effect, and the more abundantly the crystal agglomerates containing single crystals having a low Miller index facet are produced. Similar graphs for different solvents / catalysts and applied pressures can be made to determine what conditions cause the Wolf effect to prevail.

Particles having a high ratio of the surface having a high Miller Index are more easily obtained faceted crystals than particles having a high ratio of the surface having a high Miller Index. In addition, particles with low proportions of surfaces with high Miller indices may exhibit facets that are only partially cut and / or degraded.

In order to grow the crystals, the elevated temperature and elevated pressure conditions depend on the nature of the crystal. For diamond crystals, the elevated temperature is generally 1100-1500 ° C. and the elevated pressure is generally 4.5-7 GPa.

Crystals, in particular diamond crystals, can be recovered from reaction agglomerates using methods known in the art. For example, most practice methods simply decompose the solvent / catalyst remaining in the crystal mass. If some of the crystals are loosely bound to other crystals, they can be broken down by applying light milling or other similar methods.

The method described above is mainly used to produce agglomerates of crystals of size less than 100 microns. However, the method can also be used to produce agglomerates of large sized facet crystals that are visible to the naked eye, which also forms part of the present invention.

The raw crystals may be provided by particles of irregular shape that are substantially free of visually observable faceted surfaces. Examples of suitable raw material crystals are milled products. As an example, FIG. 4 shows a 260-fold magnification of the raw raw diamond crystals. The raw particles may also be provided by particles that have been treated such that the visually observable facet is damaged or destroyed and / or a surface with a high Miller index is produced to produce a higher surface energy facet.

The raw material crystals may have a narrow size distribution or a relatively wide size distribution. If the conditions are chosen such that the wolf effect prevails in crystal growth, the resulting faceted single crystal agglomerates will essentially have the same size distribution as the raw crystals.

Supersaturation can also be aided by the difference in solubility between modified and less modified (or unmodified) crystals.

The faceted diamond crystal agglomerate has abrasion, lapping and grinding applications, and is easier and more precisely to size and crystallize and has better flow properties in dry powder and slurry form. The faced diamond crystals also have applications for the production of polycrystalline articles.

The present invention relates to the growth of diamond, equiaxed boron nitride and other crystals under high temperature and high pressure conditions.

1 is a graph showing the temperature dependence of the wolf effect on diamond maintained in about 5.4 GPa for 1 hour and iron-nickel solvent / catalyst.

FIG. 2 is a graph showing the temperature dependence of the wolf effect on diamond maintained in about 5.4 GPa for 10 hours and iron-nickel solvent / catalyst.

3 is a graph comparing the recovered diamond particle size distribution with the starting diamond particle size distribution.

4 is a 260 times magnified photograph of the raw material diamond crystals.

FIG. 5 is a 260 times magnified photograph of faceted diamond crystals and some diamond twins prepared by the method of the present invention. FIG.

6 is a 520 times enlarged view of the crystal of FIG. 3.

The present invention relates to the growth or synthesis of crystals using high temperature and high pressure conditions. In particular, the present invention relates to the growth or synthesis of ultrahard abrasive particles such as diamond and equiaxed boron nitride.

The size of the raw crystals depends on the nature of the grown crystals.

The raw material crystals are applied to particles comprising a coating of a suitable material, such as a diamond core and a solvent / catalyst layer, when the diamond particles with the core have a high Miller index surface and there is substantially no visible facet. May also be provided.

The raw crystals may also be provided by particles comprising a core of any material having a cladding or covering of growth crystals.

The solvent / catalyst used depends on the nature of the growth crystals. Examples of such solvents / catalysts for diamond include transition metal elements such as iron, cobalt, nickel, manganese and alloys containing any one of these metals, stainless steel, superalloys (eg cobalt, nickel and iron-based alloys), Silicon steel, bronze, and braze such as nickel / phosphorus, nickel / chromium / phosphorus and nickel / platinum. Other suitable solvents / catalysts for diamond synthesis are, for example, elements, compounds and alloys that do not contain transition metals such as copper, copper / aluminum and phosphorus, and nonmetallic materials or mixtures thereof, such as alkalis, alkalis Earth metal hydroxides, carbonates and sulfates, chlorates and silicates (e.g., phosphate and enstatite in hydrated form).

For diamond, the raw particles may be synthetic diamonds made by conventional high pressure / high temperature processes or other suitable techniques, or by natural diamond.

The elevated temperature and elevated pressure conditions used in the method also depend on the nature in which the crystals are grown. For diamond and equiaxed boron nitride growth, the synthesis conditions are such that the crystals are thermodynamically stable. Such conditions are well known in the art. However, it is also possible to carry out diamond growth under conditions outside the thermodynamically stable range of the diamond. If Ostwald's law dominates the growth process rather than the Ostwald-Volmer law, temperature and pressure conditions outside the thermodynamically stable range of diamond may be used (Bohr, R Haubner and B Lux Diamond and Related Materials). volume 4, pages 714-719, 1995]). According to Ostwald's law, when energy is released from a system with varying energy levels, the system does not directly reach a stable ground state, In addition, according to the Ostwald-Wolmer law, a low-density phase is formed first (forming a nucleus), and if the two laws contradict each other, the Ostwald-Wolmer law is called the Ostwald. Take precedence over the law ". For diamond crystal growth outside the thermodynamically stable range, the Ostwald-Wolmer law can be suppressed, for example, by applying pressure, and grows diamond in diamond particles already present when the graphite crystal is substantially absent. Although isothermal and isostatic conditions are not essential in the practice of the present invention, these conditions are preferred.

The raw crystals are contacted with a suitable solvent / catalyst to produce reaction agglomerates. Generally, the raw crystals are mixed with the catalyst / solvent in particulate form.

The contents may be placed at elevated temperature and elevated conditions necessary to place the reaction agglomerate in a reaction zone of a conventional high temperature / high pressure device to achieve crystal growth. Surfaces with higher Miller indices are preferably dissolved in the catalyst / solvent for surfaces with lower Miller indices. Solutes migrate to surfaces with lower Miller indices and settle or grow on them. The resulting crystals have a form that depends on the saturation-time form used. Temperature and pressure conditions and the chemical composition of the solvent / catalyst also influence the morphology.

Crystallization and crystal structure modifiers such as nitrogen, boron or phosphorus may be introduced into the reaction mass to achieve a particular purpose.

The invention is illustrated by the following non-limiting examples.

Example 1

Multiple faceted diamond crystals were prepared with some twins using the reaction capsules described above. A mixture of (a) 50 g of diamond particles and (b) 285 g of iron-cobalt powder prepared by pulverizing an irregular synthetic material with a particle diameter of 20 to 40 µ was made. The diamond particles did not have a facet visible to the naked eye. The mixture was placed in a reaction capsule and the conditions increased to about 5.5 GPa and about 1420 ° C. The conditions were maintained for 11 hours. The resulting crystals were almost entirely faced and some were twins. The total crystal mass recovered was 41 g and the size range was substantially 30-50 μ. At least 80% of the particle agglomerates were single crystals.

Fig. 4 is a 260 times magnification photograph of raw diamond particles (crystals) showing the grainy (unfaced) properties of the particles. 5 and 6 are respectively enlarged photographs of the faceted diamond crystals and some diamond twins produced by the method. The facet can be clearly seen in the picture. Note that the faced crystals and twins are loosely bound into agglomerates. The agglomerates can be milled lightly or applied in a similar manner to free individual particles.

Example 2

The reaction capsules described above were used again to produce a number of faced diamond crystals. A mixture of (a) 50 g of diamond particles and (b) 284.6 g of cobalt-iron solvent was prepared by grinding an irregular synthetic material having a maximum size of 8 μ and a minimum size of 4 μ. The diamond particles did not have a facet visible to the naked eye. The mixture was placed in a reaction capsule and the conditions increased to about 5.5 GPa and about 1370 ° C. This condition was maintained for 11 hours. The grown crystals are entirely faced, some are twin, and range in size from about 6 microns to about 10 microns. 39.5 g of total crystal mass was recovered. At least 80% of the particle agglomerates were single crystals.

Example 3

Multiple faceted diamond crystals were also prepared using the reaction capsules described above. A mixture of (a) 30 vol% of diamond particles prepared by pulverizing an irregular synthetic material with a particle size distribution of 20 to 40 µm and (b) 70 vol% of iron-nickel powder was made. The diamond particles did not have a facet visible to the naked eye. The mixture was placed in a reaction capsule and the conditions increased to about 5.5 GPa and about 1400 ° C. This condition was maintained for 20 minutes. The resulting crystals are totally faced and some are twin, with a size range of 25 to 45 microns. At least 80% of the particle agglomerates were single crystals.

Example 4

The reaction capsules described above were used again to produce a number of faced diamond crystals. A mixture of (a) 30% by volume of natural diamond particles having an irregular shape with a particle size distribution of 20 to 40μ, and (b) 70% by volume of cobalt-iron powder was prepared. The diamond particles did not have a facet visible to the naked eye. The mixture was placed in a reaction capsule and the conditions were increased to about 5.5 GPa and about 1370 ° C. and the conditions were maintained for 1 hour. The recovered crystals were entirely faced and some were twins. The size of the crystals was 25-50μ. At least 80% of the particle agglomerates were single crystals.

In Examples 2, 3 and 4, the raw and faced diamond crystals and diamond twins are similar to those illustrated in FIGS. 4 and 5 and 6, respectively.

Examples 5-25

Faceted diamond crystals were prepared using other solvents / catalysts in addition to those specified in Examples 1-4. Examples of other solvent / catalyst systems, and the conditions used, are shown in Table 1 below. In each of Examples 5 to 25, the raw diamond particles were crushed synthetic diamond particles that were irregularly shaped and without the visually visible facet.

Examples 26 to 32

The invention is further illustrated by Examples 26-32, where examples of raw diamond size ranges are presented. All raw diamonds did not have a visually observable facet. The above example also illustrates the need to vary the type of solvent / catalyst in addition to the more extreme conditions for temperature and time to practice the invention at more irregular raw diamond sizes. Faceted diamond crystals were produced. The conditions used in the examples are shown in Table 2 below.

Example 33

The particle size distribution of the raw diamond agglomerates having a nominal size range of 30 μ to 45 μ and no visually visible facet was measured using laser light diffraction. A mixture of (a) 25 vol% of the raw diamond particles and (b) 75 vol% of the iron-nickel powder was made. The mixture was placed in a reaction capsule and the conditions were increased to about 5.3 GPa and about 1360 ° C. for 18 minutes.

Diamond was recovered from this material by dissolving the solvent / catalyst in a dilute inorganic acid mixture. After washing and drying, the recovered diamond was weighed and the particle size distribution was measured again.

The lost diamond mass was found to be 24% or 3.5% of the solvent / catalyst mass that is appropriate for the solubility of the diamond in the solvent / catalyst. The particle size distribution of faceted diamond recovered from the raw diamond particles and the reaction capsule is shown in FIG. 3. The particle size distributions of the raw diamond and recovered faceted diamond are substantially the same, and are also somewhat reduced from 0.178 m 2 / g to 0.168 m 2 / g at the specific surface area so that the recovered diamond is somewhat larger than the raw diamond. The somewhat irregularity of the size distribution is evidence of the facet due to the growth process using the Wolf effect rather than the dissolution process.

Example 34

Raw synthetic diamond particle agglomerates having no visually visible facet with a nominal size range of 24 μm to 48 μm were coated with a layer having about 2 μm thick nickel-phosphorus. The layer was deposited using electrolysis in such a way that the coated particles were substantially separated. A mixture comprising (a) 20% by volume of the coated diamond particles and (b) 80% by volume of sodium chloride was made and placed in the reaction capsule. The conditions of the reaction capsule were increased to about 5.2 GPa and about 1310 ° C. for 300 minutes. Diamond was recovered from the reaction capsule by dissolving sodium chloride in warm water. The recovered diamond was tested and found to be almost entirely faceted.

Example 35

A mixture of (a) 30% by volume synthetic diamond particles with no visible facet with a particle diameter of less than 0.5μ, and (b) 70% by volume of cobalt powder was made. The mixture was placed in a reaction capsule and the conditions increased to about 4.8 GPa and 1170 ° C. and maintained for 11 hours. Diamond was recovered from the reaction capsule by dissolving cobalt in dilute hydrochloric acid and filtering the diamond from solution. Diamonds were tested to observe faced crystals having a size substantially less than 1 micron. According to Munke ("Diamond Properties" edited by JE Field, page 517, Academic Press 1979), the eutectic point in the Co-C system at 4.8 GPa is about 1375 ° C and the conditions presented in the above examples. Under the reaction mixture was in a solid state during the crystal growth period.

Unless stated otherwise, the faceted diamond particles in all the examples described above were recovered by simply dissolving the catalyst / solvent in a suitable known acid or solvent remaining in each separate faceted diamond crystal agglomerate. If some of the crystals were loosely bound to others, the combined agglomerates were subjected to mild milling or a similar manner to free the crystals.

The faceted diamonds of Examples 5 to 35 were all similar to those illustrated in FIGS. 4 and 5. In all cases, there were some twins, but at least 80% of the particles were single crystals.

Claims (9)

Crystal agglomerates in which the crystal size is less than 100 microns and most of the crystal agglomerates are faceted single crystals. The method of claim 1, More than 80% of the crystal grains are faceted single crystals. The method according to claim 1 or 2, A crystal mass where the crystal is a diamond crystal. Providing a growing form of crystalline raw material that is substantially free of a visually visible faceted surface; Preparing a reaction aggregate by contacting the raw material with a suitable solvent / catalyst; Subjecting the reaction agglomerates to elevated temperatures and elevated pressures suitable for crystal growth within the reaction zone of a high temperature / high pressure device; Removing reaction agglomerates from the reaction zone; And Recovering crystals from the reaction mass, Wherein said crystal growth condition is a visually observable faceted single crystal in which the raw material crystal is selected to be converted to a crystal having a naked face observable developed facet having a low Miller index. The method of claim 4, wherein And wherein the crystal agglomerate contains at least 80% of faceted single crystals that are visible to the naked eye. The method of claim 5, How the crystal is a diamond crystal. The method of claim 6, The elevated temperature is from 1100 to 1500 ° C. and the elevated pressure is from 4.5 to 7 GPa. The method according to any one of claims 4 to 7, The supersaturation motive force required for crystal growth is predominantly caused by the difference in surface free energy between the low Miller indices and the high Miller indices of the raw crystals. The method according to any one of claims 4 to 8, How the Wolf effect prevails.